1. Field of the Invention
The present invention relates to an optical system for providing optical magnification.
2. Description of the Related Art and Background
From a historical perspective, conventional telescopes and binoculars are some of the earliest demonstrated forms of optical magnifiers. In general, these tend to be afocal magnifiers as they are viewed directly with the human eye. Binoculars include two telescope systems—one for each eye. In order to present an erect magnified image, binoculars employ telescope design forms such as the Galilean telescope as shown in FIG. 1, or an erecting telescope as shown in FIG. 2. The earliest telescopes and binoculars from the 17th century employed the Galilean form; with a positive power objective lens 11 and a negative power eyepiece lens 12 as shown in FIG. 1. The magnification of the telescope is calculated as the ratio of the focal lengths M=F/f, and the separation between the lenses is given by F-f. The advantage of this design form is its simplicity and that it provides an inherently erect and magnified image. Furthermore, it is lighter and more compact than an erecting telescope such as shown in FIG. 2. Disadvantages include a narrow field of view, an inability to achieve high magnifications, and that it is still relatively heavy and bulky. Generally, Galilean telescopes are limited to magnifications less than approximately 4×, and today are found in very limited applications such as “opera glasses”, head-worn binocular vision aids for people with eye problems such as macular degeneration, and inexpensive binocular models.
The vast majority of binoculars manufactured and sold today employ an erecting telescope, such as shown in FIG. 2. FIG. 2 shows a telescope including a positive objective 21 and a positive power eyepiece lens 22. The purpose of the pair of Porro prisms 23 is to invert the image formed by the telescope. Without the Porro prisms, the magnified image would appear to be upside down to the person using the binoculars. Manufacturers also use roof prisms as an alternative to Porro prisms. The erecting telescope is capable of high magnifications and relatively wide fields of view, when compared with the Galilean telescope. They are, however, bulky and heavy, and for these reasons are not generally practical or used for head-mounted applications.
Observers of an event, in particular sports fans, concert-goers and opera-goers, often use binoculars to observe the event from a distance. Binoculars are typically operated with one or both hands. This is sometimes problematic, for example, during a sporting event, since a sports fan cannot simultaneously watch the game through binoculars and perform other activities that require the use of hands.
Until recently, various hands-free binoculars have been proposed, but they are often expensive and not optimally designed in form and function for the requirements of the sports fan, concert-goer or opera-goer in mind. For example, U.S. Pat. No. 2,422,661, issued Jun. 24, 1947 to C. A. Ellis, describes a binocular magnifying lens holder. U.S. Pat. No. 2,437,642, issued Mar. 9, 1948 to F. C. P. Henroteau, describes spectacles for vision correction. U.S. Pat. No. 3,741,634, issued Jun. 26, 1973 to Stoltze, describes binocular spectacles.
Further, U.S. Pat. No. 4,429,959, issued Feb. 7, 1984 to Walters, describes a spectacle mounted hinged monocular or binocular vision aid. U.S. Pat. No. 5,485,305, issued Jan. 16, 1996 to Johnson, describes a lightweight binocular telescope. U.S. Pat. No. 6,002,517, issued Dec. 14, 1999 to Elkind, describes flat, hands-free, convertible Keplerian binoculars.
Some of the most sophisticated head-worn binoculars available today are the head-worn binocular vision aids for people with eye problems such as macular degeneration. They are still relatively bulky which affects their wider acceptance for broader applications, and their weight is significant as well. The Eschenbach Model 1634 is an example of this type of binocular magnifier, with a magnification of 3×, a field of view of 9.5 degrees, and a weight of 70 grams. These binoculars are typically mounted in a pair of custom spectacle frames. Generally, the nearest optical surface to the eye for a pair of spectacles or head-mounted optics is approximately 15 mm in front of the eye. The telescopes then extend a further 20-25 mm from the eye in the case of the Eschenbach 1634 model as an example. This significant weight at a distance from the eye tends to exert a torque on the head and leads to neck strain when used for extended viewing periods.
In order to reduce the weight of the head-worn binoculars, one of the approaches employed has been to use all plastic optics rather than glass lenses as normal, and some models have used a Fresnel lens for the objective. This does serve to reduce the overall weight, but still has the same basic form as in FIG. 1 with a single positive objective lens and a single negative eye lens. So, the length of the telescope is still the same, making it rather bulky and unwieldy, and is a limitation of this design approach. Design models using this approach include the MAX TV and MAX Event models from Eschenbach.
Feldman disclosed a new form of optical magnifier in U.S. Pat. No. 6,226,120 that consists of a single array of Galilean telescopes for each eye mounted in a pair of spectacle frames. The form of the Galilean telescope employed by Feldman is shown in FIG. 3. This invention overcomes some of the limitations of a standard Galilean telescope, which is by nature heavy and bulky as discussed. The Feldman system by contrast is lightweight and compact, but has severe limitations due to the use of a single array of lenses; the optical performance of such a system is poor and may be unusable in many applications, suffering from large amounts of chromatic aberration, spherical aberration and off-axis aberrations such as coma and astigmatism. We know of no way to correct for these aberrations using a single array as disclosed by Feldman.
Wirth et al. in U.S. Pat. No. 5,270,859 discuss configurations of micro-optic multiplets (MOM) which include an array of Galilean telescopes as reproduced in FIG. 4. This design form suffers from an inability to simultaneously correct chromatic aberrations and aberrations arising from thermal expansion, which can result in poor imaging.
It is an object of this invention to provide an improved more compact optical design form allowing better correction of optical aberrations and consequently better image performance than offered in the aforementioned prior art devices.
It is a further object to provide an improved mounting method; and, an optical system having enhanced performance over a wide range of thermal environments.
The applications for this invention are many, including, but not limited to, a wide-angle attachment for camera systems, afocal magnifier for rifle scopes and night vision systems, telescope and binocular systems, and others as will be obvious to those skilled in the art.